158 research outputs found
The Structure of the X-Ray Emitting Gas in the Hydra-A Cluster of Galaxies
The temperature and abundance structure in the intracluster medium (ICM) of
the Hydra-A cluster of galaxies is studied with ASCA and ROSAT. The effect of
the large extended outskirts in the point-spread function of the X-Ray
Telescope on ASCA is included in this analysis. In the X-ray brightness
profile, the strong central excess above a single beta-model, identified in the
Einstein and ROSAT data, is also found in the harder energy band (>4keV). A
simultaneous fit of five annular spectra taken with the GIS instrument shows a
radial distribution of the temperature and metal abundance. A significant
central enhancement in the abundance distribution is found, while the
temperature profile suggests that the ICM is approximately isothermal with the
temperature of ~3.5keV. The ROSAT PSPC spectrum in the central 1'.5 region
indicates a significantly lower temperature than the GIS result. A joint
analysis of the GIS and PSPC data reveals that the spectra can be described by
a two temperature model as well as by a cooling flow model. In both cases, the
hot phase gas with the temperature of ~3.5keV occupies more than 90% of the
total emission measure within 1'.5 from the cluster center. The estimated mass
of the cooler (0.5-0.7keV) component is ~2-6 x 10^9 M_solar, which is
comparable to the mass of hot halos seen in non-cD ellipticals. The cooling
flow model gives the mass deposition rate of 60+-30 M_solar/yr, an order of
magnitude lower than the previous estimation.Comment: 27 pages, 14 figures, AAS LATEX macros v4.0, to appear in The
Astrophysical Journa
Unusual diffuse X-ray source in the Galactic center region
We report the ASCA and Chandra discovery of a diffuse X-ray source in the
Galactic center region. The X-ray spectrum is fitted with a non-equilibrium
ionization (NEI) plasma model of about 6-keV temperature. The model requires
higher than solar metal abundances, a young plasma age of 100 years
and a large N_H value of about 10^{23} cm^{-2}. The N_H value constrains the
source position to be in the Galactic center region at about 8.5 kpc distance.
The high resolution X-ray image with the Chandra ACIS shows a ring of 10''
radius which corresponds to 0.4 pc at the Galactic center, and a tail-like
structure. Although the morphology is peculiar, the other X-ray features are
likely to be a very young supernova remnant, possibly in a free expansion
phase.Comment: 11 pages, 4 figures, to be published in Ap
ASCA Observations of the Sgr B2 Cloud: An X-Ray Reflection Nebula
We present the ASCA results of imaging spectroscopy of the giant molecular
cloud Sgr B2. The X-ray spectrum is found to be very peculiar; it exhibits a
strong emission line at 6.4 keV, a low energy cutoff below about 4 keV and a
pronounced edge-structure at 7.1 keV. The X-ray image is extended and its peak
position is shifted from the core of the molecular cloud toward the Galactic
center by about 1--2 arcminute. The X-ray spectrum and the morphology are well
reproduced by a scenario that X-rays from an external source located in the
Galactic center direction are scattered by the molecular cloud Sgr B2, and come
into our line of sight. Thus Sgr B2 may be called an X-ray reflection nebula.
Possible implications of the Galactic center activity related to this unique
source are presented.Comment: 15 pages, 8 figures, AAS LaTeX, To be published in The Astrophysical
Journa
ASCA Discovery of Diffuse 6.4 keV Emission Near the Sgr C Complex: A New X-ray Reflection Nebula
We present an ASCA discovery of diffuse hard X-ray emission from the Sgr C
complex with its peak in the vicinity of the molecular cloud core. The X-ray
spectrum is characterized by a strong 6.4-keV line and large absorption. These
properties suggest that Sgr C is a new X-ray reflection nebula which emits
fluorescent and scattered X-rays via irradiation from an external X-ray source.
We found no adequately bright source in the immediate Sgr C vicinity to fully
account for the fluorescence. The irradiating source may be the Galactic
nucleus Sgr A*, which was brighter in the past than it is now as is suggested
from observations of the first X-ray reflection nebula Sgr B2.Comment: 10 pages, 2 figures, AAS LaTeX, To be published in The Astrophysical
Journa
ASCA X-ray source catalogue in the Galactic Center region
The ASCA satellite made 107 pointing observations on a 5 x 5 deg^2 region
around the center of our Milky Way Galaxy (the Galactic Center) from 1993 to
1999. In the X-ray images of the 0.7--3 keV or 3--10 keV bands, we found 52
point sources and a dozen diffuse sources. All the point sources are uniformly
fitted with an absorbed power-law model. For selected bright sources, Sgr A*,
AX J1745.6-2901, A 1742-294, SLX 1744-300, GRO J1744-28, SLX 1737-282, GRS
1734-292, AX J1749.2-2725, KS 1741-293, GRS 1741.9-2853, and an unusual flare
source XTE J1739-302, we present further detailed spectral and timing analyses,
and discuss their nature.
The dozen extended X-ray sources comprise radio supernova remnants, giant
molecular clouds, and some new discoveries. Most show emission lines from
either highly ionized atoms or low-ionized irons.
The X-ray spectra were fitted with either a thin thermal or power-law model.
This paper summarizes the results and provides the ASCA X-ray source catalogue
in the Galactic Center region.Comment: 33 pages, 8 figures, Accepted for publication in ApJS, also found in
http://www.star.le.ac.uk/~mas/research/paper/#Sakano2001apj
Zn-Neighbor Cu NQR in Zn-Substituted YBa2Cu3O7-d and YBa2Cu4O8
We studied local electronic states near Zn in optimally doped
YBa(CuZn_x)O and underdoped
YBa(CuZn_x)O via satellite signals of plane-site Cu(2)
nuclear quadrupole resonance (NQR) spectra. From the relative intensity of Cu
NQR spectra, the satellite signals are assigned to Zn-neighbor Cu NQR lines.
The Cu nuclear spin-lattice relaxation time of the satellite signal is shorter
than that of the main signal, which indicates that the magnetic correlation is
locally enhanced near Zn both for the underdoped and the optimally doped
systems. The pure YBaCuO is a stoichiometric, homogenous,
underdoped electronic system; nevertheless, the Zn-induced inhomogeneous
magnetic response in the CuO plane is more marked than that of the
optimally doped YBaCuO.Comment: 9 pages including 8 figures, to be published in Phys. Rev.
phi photo-production from Li, C, Al, and Cu nuclei at Egamma=1.5 - 2.4 GeV
The photo-production of mesons from Li, C, Al, and Cu at forward
angles has been measured at =1.5--2.4 GeV. The number of events for
incoherent phi photo-production is found to have a target mass number
dependence of in the kinematical region of
. The total cross section of the -nucleon interaction,
, has been estimated as mb using the
-dependence of the photo-production yield and a Glauber-type multiple
scattering theory. This value is much larger than in free
space, suggesting that the properties might change in the nuclear
medium.Comment: 12 pages 4 figures, submitted to Phys. Lett.
Visual function and serous retinal detachment in patients with branch retinal vein occlusion and macular edema: a case series
<p>Abstract</p> <p>Background</p> <p>The influence of serous retinal detachment (SRD) on retinal sensitivity in patients with branch retinal vein occlusion (BRVO) and macular edema remains unclear. This is despite the frequent co-existence of SRD and cystoid macular edema (CME) in BRVO patients on optical coherence tomography (OCT) and the fact that CME is the most common form of macular edema secondary to BRVO. We investigated visual function (visual acuity and macular sensitivity), macular thickness, and macular volume in patients with BRVO and macular edema.</p> <p>Methods</p> <p>Fifty-three consecutive BRVO patients (26 women and 27 men) were divided into two groups based on optical coherence tomography findings. Macular function was documented by microperimetry, while macular thickness and volume were measured by OCT.</p> <p>Results</p> <p>There were 15 patients with SRD and 38 patients with CME. Fourteen of the 15 patients with SRD also had CME. Visual acuity was significantly worse in the SRD group than in the CME group (P = 0.049). Also, macular thickness and macular volume within the central 4°, 10°, and 20° fields were significantly greater in the SRD group (P = 0.008, and P = 0.007, P < 0.001 and P < 0.001, and P < 0.001 and P < 0.001, respectively). However, macular sensitivity within the central 4°, 10°, and 20° fields was not significantly worse in the SRD group than in the CME group.</p> <p>Conclusions</p> <p>SRD itself may decrease visual acuity together with CME, because nearly all SRD patients also had CME. SRD does not seem to influence macular function on microperimetry.</p
Superconducting Fluctuation investigated by THz Conductivity of LaSrCuO Thin Films
Frequency-dependent terahertz conductivities of LaSrCuO thin
films with various carrier concentrations were investigated. The imaginary part
of the complex conductivity considerably increased from far above a
zero-resistance superconducting transition temperature,
, because of the existence of the fluctuating
superfluid density with a short lifetime. The onset temperature of the
superconducting fluctuation is at most for
underdoped samples, which is consistent with the previously reported analysis
of microwave conductivity. The superconducting fluctuation was not enhanced
under a 0.5 T magnetic field. We also found that the temperature dependence of
the superconducting fluctuation was sensitive to the carrier concentration of
LaSrCuO, which reflects the difference in the nature of the
critical dynamics near the superconducting transition temperature. Our results
suggest that the onset temperature of the Nernst signal is not related to the
superconducting fluctuation we argued in this paper.Comment: J. Phys. Soc. Jpn. in pres
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